Planning for RHIC II and eRHIC

Today, the ultra-high temperatures of the early universe are
approachable on Earth — but only inside the largest, highest energy
particle accelerators. That is why the
Relativistic Heavy Ion Collider
(RHIC) was constructed at Brookhaven National Laboratory: to attempt to
recreate quark-gluon plasma, a state of matter that is thought to have
existed immediately after the Big Bang.

Once the existence of quark-gluon plasma is proven, however, two
challenges will remain. The first is to characterize this primordial state
of matter and its relationship to the fundamental features of today’s
universe. The second is to look for color glass condensate. It is
hypothesized to be the saturated, or maximum density, state that can be
achieved at high energies by particles subject to the strong force, which
is the short-range attraction binding atomic nuclei.

To undertake these tasks, Brookhaven has proposed and the U.S.
Department of Energy is planning for two upgrades to RHIC: RHIC II and
eRHIC.

RHIC II

The RHIC II upgrade will provide a ten-fold increase in the
luminosity, or collision rate, enabling scientists to study particle
collision events that happen only rarely and to explore states of matter
believed to have existed during the first moments after the Big Bang.
- Facilities for the Future of Science: A 20-Year Outlook Office of
Science, U.S. Department of Energy

Although RHIC’s gold-ion beams are energetic and intense enough for the
plasma’s discovery and initial exploration, beams of even higher intensity
are needed for a detailed examination of rare processes.

By upgrading RHIC into RHIC II, the collider’s luminosity, or collision
rate, will be increased by a factor of ten, thereby increasing the rate of
plasma production and the ability to study rare processes associated with
the substance.

After examining the science intersecting physics and astronomy, the
National Research Council of the National Academy of Sciences identified
the existence of quark-gluon plasma as one of the most pressing research
questions to be addressed in this field. In addition, the science
underlying RHIC II received the highest ranking from a future-facilities
subcommittee of the Nuclear Science Advisory Committee (NSAC), which
reports to DOE’s Office of Science and to the National Science Foundation.

eRHIC

The addition of an electron accelerator to the current RHIC facility
would create the world’s first electron-heavy ion collider,
enabling the creation of an enormous number of gluons and presenting a
unique opportunity to probe the substructure of particles.
- Facilities for the Future of Science

Since color glass condensate is another form of matter thought to exist
in heavy nuclei accelerated to high energy, Brookhaven has proposed to
turn RHIC into eRHIC, the world’s only electron-heavy ion collider.

Point-like and weakly interacting, the electron is an ideal probe of
nuclear structure. Evidence from lower energy electron accelerators has,
in fact, resulted in the prediction of color glass condensate. Some think
that, before nuclei colliding at high energy can make quark-gluon plasma,
they become densely compressed — a color glass condensate — in the
direction they are being accelerated. Upon impact, color glass condensate
is thought to “shatter,” thus forming the plasma.

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